http://caselaw.lp.findlaw.com/data/constitution/amendment09/The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage
others retained by the people.
Emphasis mine.
I would say this phrase includes the right to ingest any substance, since tobacco was smoked at the time of ratification of the Constitution as well as this Amendment.
I am not for broad-spectrum drug use; however, outright prohibition does indeed fall afoul of this Amendment. Regulation, as for alcohol and tobacco, is the only Constitutional remedy.
The so-called "War on Drugs" is therefore unconstitutional, since the government could simply regulate it, as noted.
Bwahah.
edited to add: this would include a right to privacy, also mentioned in the the 4th Amendment as the right to be secure in one's own person, houses, papers, and effects. It could in fact be argued that the right to privacy is actually an enumerated right, by virtue of another Amendment.